The present invention relates to portable instruments for the testing of valve characteristics and, more particularly, to a portable testing system for the purpose of testing implantable valves to determine the pressure and flow characteristics of these valves. In particular, this invention is useful in the testing of ventricular shunt valves immediately prior to surgical implantation.
The variety and number of implantable valves used to treat medical conditions in the human body has increased tremendously over the past decade. Hydrocephalus is one such medical condition that often requires the use of a valve implanted into the patient's body, particularly within the brain tissue. Hydrocephalus is the general term that characterizes the condition in which the body, for any one of a variety of reasons, is unable to relieve itself of excess cerebrospinal fluid (CSF) collected in open spaces (ventricles) that are found in the brain. Excessive collection of the CSF in the brain ventricular spaces can and quite often does result in an increase in pressures on the brain both radially outwardly and radially inwardly. Acute or unexpected increases in these brain pressures are known to cause a number of adverse physiological effects including compression of brain tissue, internal blood flow in the brain tissue, and impairment of the normal metabolism of the brain.
Treatment of a hydrocephalic condition therefore requires the relief of any abnormally high pressures that may arise within the skull. This is most easily accomplished by providing a means for the drainage of the excess fluid. As a result, a variety of valves for the use in CSF pressure regulator systems and in methods of controlling CSF pressure have been developed. These valves can take various forms such as single and dual check valves, servo valves or combinations thereof. Since CSF is essentially an ultrafiltrate of blood, such valves usually divert CSF from the ventricles of the brain through a discharge line to a suitable drainage area within the patient's body, such as the venous system or the peritoneal cavity. However, the CSF can also be directed to an area exterior of the body so that the flow of the fluid can be monitored and the fluid contents analyzed. Check valves are most often used in these drainage systems and these valves operate by opening when the difference between the pressure of the CSF within the cranial area of the patient exceeds the pressure in the outlet or discharge line.
Valves that are implantable in the body therefore require testing to determine their operating characteristics such as the pressures at which the valve will open and close for given flow rates. These characteristics can then be compared to the patient's requirements and may also be helpful in providing a confirmation of the valve design specifications prior to implantaion. The operating characteristics of an implantable valve encompass both the pressures at which the valve will open continuously, and the pressures at which the valve will only open momentarily for intermittent flow and discharge the excess CSF fluid. With these characteristics before him, the surgeon can then make any necessary adjustments in the valve, if the valve is of the adjustable type, to match the requirements of the patient prior to implantation while in the operating room.
It therefore becomes desirable to provide a system for the testing of implantable valves. It further becomes desirable to provide a portable and compact system for testing implantable valves for use within the operating room. Additionally, it is also desirable to provide a portable testing system for implantable valves in which the testing medium is a gaseous fluid rather than a liquid fluid which is the typical testing medium for such valve testing systems. Utilizing a liquid testing medium requires providing a reservoir of the liquid testing medium and maintaining the sterility of such a liquid testing fluid.
The present invention is directed to a system for the testing of implantable valves using air or a similar gaseous fluid as a testing medium to determine the pressure and flow characteristics of such valves. In such a testing system, a pump is provided to pump a testing fluid drawn from the testing environment under sterile conditions, through the implantable valve. A control mechanism is attached to the pump for providing a variety of constant flow rates so that the characteristics of the valve can be determined under a variety of operating conditions. A pressure transducer that utilizes atmospheric pressure as a reference senses the changes in the air pressure in the valve. The transducer is coupled to a signal generator which generates a signal that is received by a recording instrument. The recording instrument preferably is provided with both a digital display recorder and a chart recorder or plotter to provide a permanent record of the pressure/flow characteristics of the valve which may be preserved and attached to the patient's chart.
The use of air or similar gaseous fluid as a testing medium dispenses with the need for a liquid fluid reservoir thus giving the testing system of the present invention its desired portability. By the use of air or the like for testing purposes, the need to dry or disinfect the valve is eliminated. A filter element that includes a bacteriostatic filter may be provided between the valve and the pump to prevent entrance of any airborne contaminants into the valve. Typically, sterile tubing will be used in the system so that the pressures and pressure versus flow characteristics can be determined in a sterile field such as that which one obtains in an operating room.
In view of the foregoing, it is a general object of the present invention to provide a new and improved system for testing the pressure/flow characteristics of implantable valves.
It is another object of the present invention to provide a portable test system for the testing of the pressure/flow characteristics of ventricular shunt valves utilizing a gaseous fluid as a testing medium.
It is a further object of the present invention to provide a portable instrument system for testing the pressure/flow characteristics of ventricular shunt valves in which the test system includes a single pressure sensing device having atmospheric pressure as a reference point.
It is yet a further object of the present invention to provide a portable instrument system for testing the pressure/flow characterisitcs of implantable ventricular shunt valves having a variety of selectable constant flow rates for delivering air to a surgically implantable valve such that the valve can be calibrated within the sterile field of an operating room.
It is still a further object of the present invention to provide a portable testing system for the testing of implantable valves wherein the testing system may be placed outside the sterile field of the operating room and by sterile fluid communication means, an implantable valve can be tested in the operating room without breaking the sterile field.